Despite significant advances in molecular simulations, it is still very challenging, if not impossible, to study nanoparticles in a given solvent and get molecular details about the arrangement of solvent molecules around the nanoparticles as well as the forces between nanoparticles in solutions. In this work, we use classical density functional theory (cDFT) to study nanoparticles in water-like solvents and investigate the solvent density profiles around nanoparticles and the potential of mean forces between nanoparticles of various sizes up to 50 nm radius. We validate the accuracy of cDFT calculations by comparing the results for relatively small nanoparticles with the molecular dynamics simulation results, which are possible for such sizes. We find that for silica-type nanoparticles with reasonable surface charge densities obtained from atomic force microscopy, the solvent density profiles around nanoparticles of various sizes are not significantly affected by the nanoparticle sizes. In particular, no wetting transition is observed around the nanoparticle sizes studied. As the nanoparticle sizes increase, we observe that the potential of mean forces between them can change behavior from attractive to repulsive suggesting that relatively small silica-type nanoparticles tend to attract each other in water-like solutions leading to their stability. The effects of various contributions to the potential of mean forces as well as the role of the surface charge densities on the stability of nanoparticles are also discussed.

Stability of silica-like nanoparticles in aqueous solutions

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